The overall objective of this research is to contribute to a new possible therapy in the field of cancer, particularly breast cancer, as based on the chemistry of the prolactin inhibiting factor (PIF) or hormone of the hypothalamus. The goal for the forthcoming year is to complete the isolation of the prolactin inhibiting hormone from porcine hypothalamic tissue and then to elucidate its structure and then to synthesize it. During the current year of research initial purification steps and intermediate purification steps have been largely worked out and reasonably well standardized. The current effort during the early part of 1974, is on the final purification steps to provide the pure PIF. In vitro assays have served to guide the work on isolation, and fractions which are apparently active at nanogram-microgram dosage which substantially inhibit the release of prolactin are at hand.